Electromechanical indicating system



Feb. 15, 1955 c. ca. ROPER 2,702,331

ELECTROMECHANICAL INDICATING SYSTEM Original Filed Oct. 21, 1947 3Shee'ts-Sheet l fru/irlavr- Feb. 15, 1955 c. G. ROPER 2,702,381

ELECTROMECHANIGAL INDICATING SYSTEM Original Filed Oct. 21, 1947 5Sheets-Sheet 2 Feb. 15, 1955 c, ROPER 2,702,381

ELECTROMECHANICAL IND ICATING SYSTEM Original Filed Oct. 21, 1947 3Sheets-Sheet 3 v t/sz J ezrZow- Cftayles G .Ro e r Unitcd States PatentELECTROMECHANICAL INDICATIN G SYSTEM Charles G. Roper, Fairlield, Conn.,assignor to Manning,

Maxwell & Moore, Inc., New York, N. Y., a corporation of New JerseyOriginal application October 21, 1947, Serial No. 781,066, now PatentNo. 2,614,163, dated October 14, 1952. Divided and this applicationAugust 13, 1952, Serial No.304,125

12 Claims. (Cl. 340187) This invention involves electro-mechanicalindicating systems for indicating the magnitude of any variable whichcan be represented by small electrical values such as for examplethermo-couple currents and voltages.

An object of this invention is to provide an electromechanical indicatorcapable of providing large scale indication from low level directcurrent electrical signals.

Another object of this invention is to provide an electro-mechanicalindicator of the type employing elec tro-mechanical degenerativeoperation to provide high gain stable direct current amplification forlow impedance low current inputs.

Another object of this invention is to provide an electro-mechanicalsystem for continuously indicating the value or the changing values oflow value electrical signals representative of the phenomenon beingindicated.

Still another object of the invention is to provide in a system of thistype combinations in which electrical or mechanical forces are used toproduce an amplified output by means of an electrically stabilizedrelay.

Still another object is to provide in such a system anelectro-rnechanical force-balance servo mechanism in combination with ahigh frequency oscillator wherein detuning of the oscillator produces anamplified current to actuate the indicator, and further wherein motionof the indicator is converted into a balancing force applied to theservo mechanism whereby mechanical indication is exactly weighed againstthe electrical input.

Still another object of this invention is to provide a system of thistype in which line variations in the main voltage source causenegligible error in the calibration of the instrument.

Still another object of the invention is to provide inelectro-mechanical indicators of this type an arrangement wherein largescale indication is combined with micro-ammeter sensitivity in themeasurement of small electrical value representative of the phenomenonbeing indicated.

Still another object of the invention is to provide an electro-magneticdampening means responsive to the rate of change of the indicatoractuating current to stabilize the instrument, and thereby, preventover-shooting of the indicator and reduction in its oscillation.

Other and more detailed objects of the invention will be apparent fromthe following description .of the embodiments thereof illustrated in theattached drawmgs.

This application is a division and continuation-in-part of my copendingapplication Serial No. 781,066, filed October 21, 1947, now Patent No.2,614,163, issued October 14, 1952, Reissue No. 23,850, July 13, 1954.

In the accompanying drawings,

Figure 1 is a diagrammatic and schematic illustration of anelectro-mechanical indicator for indicating changes in magnitude of lowvalue direct current input signals representative of a changingcondition to be indicated such as for example temperatures, pressures,rates of fluid flow, and the like;

Figure 2 is a similar view of a modified indicator employing a solenoidmotor as distinguished from a rotating motor to operate the indicator,further characice terized by the provision of an electro-magneticdampening means.

Figure 3 is a diagrammatic more detailed disclosure of the circuitelements and connections used in the system of Figure 2 and capable ofuse with modifications in The indicators herein disclosed employ anelectrothe system of Figure 1. mechanical de-generative system toprovide high gain stable D. C. amplification for low impedance lowcurrent inputs. It will be understood that the low impedance low currentinputs comprise electrical signals which may be representative ofvariations in any condition to be indicated, such as for example changesin temperature, pressure, rates of fluid flow, and the like. Indeed,those skilled in the art will recognize that any variable factor whichis capable of being represented by such an input signal can be indicatedwith an instrument of this type. 7

As will appear later, the indicator of this invention has a highsensitivity as it is capable of producing a change in indications with acorresponding change in electrical input as small as one-tenth of onepercent of the input range. Likewise, the indicators herein disclosedare capable of operation with negligible error with changes in linevoltage of say volts of from 95 to volts. Such variations are notinfrequently encountered in line voltages, and will cause in the systemsherein disclosed, less than three-tenths of one percent error incalibration.

The indicator of Figure 1 is diagrammatically illustrated as including agalvanometer MB consisting of a permanently magnetized field structure10 having a central pole piece 11 forming an annular magnetic field.Mounted in this field is an input coil 12 which consists of a suitablenumber of turns of wire mounted upon a cylindrical insulating formproportioned to telescope over the end of the pole piece 11. This coilform is rigidly attached to the end of a lever comprising the arms 13and 14. This lever forms a beam and is preferably of metal, providedwith a pair of upstanding tabs 15 which are either attached thereto orupstruck therefrom. These tabs are secured to the upper ends of a pairof resilient cantilever leaf springs 16 to which are also attached anarm 18. The cantilever springs 16 are anchored at their lower ends to afixed support 17, in any suitable manner so as to be rigidly supported.These leaf springs provide a resilient pivotal support for the beam 13,14 as distinguished from a pivotal support such as provided by a shaftand bearings. This construction eliminates the inherent difiicultiesencountered in pivotally supported shafts of which static friction is aparticularly undesirable and inherent disturbing factor.

At 19 is a rotatable shaft on which is mounted the pointer 24 of theindicator. Shaft 19 will, of course, be rotatably mounted in suitablebearings, not shown, for the sake of simplicity. It extends through asuitably shaped dial, in this case a circular disc 23 having acalibrated scale on the face thereof with respect to which the pointermoves.

Shaft 19 is connected to the lever 18 by means of a spiral spring 20having its inner end attached to the shaft 19 and its outer end to thelever 18. A smaller spiral spring 21 is attached to the shaft 19 at theinner end of the spring and has its outer end anchored to the fixedsupport 17. Mounted on the shaft 19 is a gear 22 which meshes with adriving pinion 25 mounted on the rotatable shaft of an electric motor26.

The end 14 of the beam terminates in a flag which is arranged to movewith respect to an oscillator coil 29 forming part of a combinedoscillator and full wave rectifier 27. The power supply is through atransformer 28 which serves to energize the oscillator and under thecontrol of the rectifier to provide an operating current to the electricmotor 26. The oscillator and rectifier functions are performed by thecombination triode and diode, the triode providing one-half of the fullwave rec- 21 is provided to provide a return force to the pointer shaft19.

The direct current input, varying in proportion to changes in thevariable to be indicated, is fed through the circuit wires 30 to theinput coil 12. The magnetic field accompanying the'flow of the currentthrough the coil 12 reacts upon the magnetic field of the permanentmagnet structure of the galvanometer, causing displacement of the lever13 forming part of the beam, and likewise the other lever 14 of the beamwith respect to the oscillator coil 29. This movement of the beam 13-14is substantially a rotary movement permitted by the resilient leafspring supports 16 for the beam intermediate its. ends. The lever 18 isrigidly attached to the beam so that geometrically its plane is at rightangles to the plane of the beam and will, therefore, be correspondinglyrotated or tipped through an angle corresponding to that through whichthe beam moves.

The movement of the flag end of lever 14 with respect to the oscillatorcoil 29 detunes the oscillator 27 and correspondingly changes its outputto provide an operating current for the alternating current motor 26 ofa magnitude related to the displacement of the beam, which displacementis caused by the difference between the force produced by the directcurrent input in the circuit 30 and the balancing or feedback forceproduced by spring 20. This current will cause the motor 26 to operatethe pointer 24 through the gears 25 and 22 to a position on the scalewhich indicates, when the scale is properly calibrated, the value of thedirect current input. Shaft 19, of course, rotates with the pointer,distorting springs 21 and 20. Distortion of spring 20 will causeapplication of a force to lever 18 to oppose the magnetic force whichdisplaced the beam 13-14, and thereby operates to reduce the power beingdelivered to the motor bringing it to rest as the forces applied to thegalvanometer are brought into balance. Thus the pointer comes to restand remains stationary until there is a change in the direct currentinput either by increase or decrease. If there is an increase in inputsignal in circuit 30 the current to the motor 26 will be increased,moving the pointer correspondingly upscale until the resultantaccumulation of stress in the spring 20 restores the galvanometer tobalance, reducing the current to the motor and bringing it to rest at anew position, indicating the change in value.

Onthe other hand, if the vaue of the direct current input decreases, theoutput of the oscillator will be correspondingly decreased, reducing thetorque generated by the motor 26, whereupon spring 21 will move shaft19, and hence the pointer 24 downscale to a point where the torqueproduced by spring 20 will again be in balance with the new value ofinput in circuit 30 and at the same time reduce the current to motor 26through the operation of the electronic control circuit, bringing themotor and pointer to rest indicating this new value. In other words,increases in the output current of the oscillator cause motor 26 todrive the pointer upscale, correspondmgly stressing spring 21, whiledecreases in the oscillator output correspondingly reduce the torque ofmotor 26, permitting stressed spring 21 to return shaft 19 and pointer24 downscale to the new value. These movements of the shaft 19, actingthrough the calibrated spring 20, serve to apply a balancing force tothe lever 18, and hence to the beam 13-14 to balance the force ofreaction of the magnetic field of coil 12 on the permanent magneticfield of the galvanometer. Of course, the stressing of leaf spring 16will form a part of this action, but within the small ranges of movementof the beam 13-14. The forces interposed by the leaf spring 16 beingsubstantially constant permit calibrated spring 20 to provide the majorand active portion of the mechanical force which balances the magneticforce of the galvanometer.

In the system of Figure 2 there is illustrated a combination generallysimilar to that of Figure 1, but dif ferent in several importantaspects. In the first place, instead of a rotary motor, that is motor 26of Figure 1, in the system of Figure 2 there is employed what may betermed a solenoid motor of which the armature rotates only through afraction of a revolution for full scale movement of the pointer. Theassociated electronic circuit has been modified to accommodate for thischange in motor characteristics. This circuit is only diagrammaticallyillustrated in Figure 2, but is shown in full detail in Figure 3. Theother main difference is that in the system of Figure 2 there isprovided electro-magnetic means for dampening the movement of the beamto prevent hunting and over-shooting of the indicator.

In this system the galvanometer MB, comprising the permanent magneticfield 10-11, the input coil 12 and the beam 13-14, is the same as in theprevious system. In this figure the pivotal support for the beam isshown diagrammatically by the fulcrum member F, but it will beunderstood that a resilient spring support like that of Figure 1 wouldnormally be used. In this arrangement,

as shown, the portion 13 of the beam is provided with a,

transversely extendnig lever 33, movable therewith. Lever 33 isconnected by a rigid link 34 to an extension shaft 19. Functionally thelever 33, the link 34. and the shaft 19' are the equivalent of the lever18 of Figure l. The inner end of a spiral spring 20 is attached to theshaft 19 and the outer end is connected by a rigid link. as shown, toone end of the pointer shaft 19, which as before is journaled insuitable bearings, not shown. The structure represented by the parts 33,34 and 19' is simply an extension from the beam 13-14, arranged toprovide a support for the center of the spring 20 so as to align thecenter of the spring 20 with the axis of rotation of the beam. Thereturn spring 21, as in the previous case, has one end anchored to afixed support and its inner end attached to the shaft 19. The inputcircuit 30 in Figure 2 is shown connected to a thermo-couple 31 inseries with which is an adiustable calibrating resistance 32. In thisarrangement instead of a rotating motor 26. a solenoid motor SM isprovided having a magnetizable field 35 of suitable shape in the air gapof which is oscillatably mounted a magnetizable armature 36. Mounted onthe armature 36 so as to be on the center of its rotation is a segmentshaped piece 37 which is connected by a cord 40 to a sleeve 39 attachedto the shaft 19. One end of the cord 40 is attached to the segment 37and the other end is attached to the sleeve 39. This type of drive isada table to this use because it permits of the assembly of the solenoidunit to the galvanometer unit without the necessity for close control oftolerances in the assembly operation.

The return spring 21 is provided in order to permit I this drive tofunction properly. The segment 36 is provided with a radial extension towh ch one end of a coiled tension spring 38 is anchored. The other endof this spring is anchored on the m tor stator. as shown. This springprovides the return force for the armature. It will be seen that spring21 provides a return force for the shaft 19 so that on return ordownscale movements the cord of the Gold belt drive will be kept undertension.

The magnetizable field structure 35 is provided with a magnetizingwinding 41, to one terminal of which a suitable current source, to bedescribed, is connected by means of the wires 43. Inductively associatedwith the winding 41 on the field structure 35 is a winding 42 which isconnected by the circuit wires 44 to the winding 84 which provides thema netic means by which the rate at which the magnetic field in winding41 is measured to apply a counterbalancing magnetic force to the beam todampen its movement. It will be understood that the windings 12 and 84are wound on a sleeve, which telescopes over the end of the cylindricalpole 11 of the galvanometer, and which is rigidly attached to the beam I13-14 for movement therewith. The oscillator is shown diagrammaticallyat 45 and in full detail in Figure 3.

The circuits of the system of Figure 2 are shown in greater detail inFigure 3. The galvanometer MB is diagrammatically illustrated ascomprising, as before, the magnetized field member 10-11, with Which isassociated the beam 13-14 on the fulcrum F, the signal input coil 12,and the oscillator tuning coil 29. In addition a dampening coil 84 iswound on the coil form which supports the input coil 12. The leads 30extend from the terminal board TB-2 to the corresponding connectors onthe terminal board TB-l, and from there to the input coil 12. Thethermo-couple or other low voltage direct current signal input source isconnected to the terminals of the terminal board TB-2, to which theleads 30 are connected. The potentiometer 32 is connected across theleads 30 to provide a calibrating resistor of suitable range.

The two remaining terminals of the terminal board TB-2, which are to beconnected to a suitable current source, such as 115 volt A. C. line,have connected thereto the leads 43 which energize the primaries P-1 andP-2 of the main transformer MT. This transformer is provided with asecondary providing two sections S-1 and 8-2 by reason of the centraltab connection 46. The outer terminals of this secondary are connectedto the plates of a pair of dual triodes 49 and 50. The grids of thesetubes are connected in parallel to a grid-biasing network 52 acrosswhich the terminals of the oscillator tuning coil 29 are connectedthrough the terminal board TB-l. One terminal of the magnetic dampeningcoil 84 is connected to ground through the terminal board TB-l and theother terminal is connected through the same terminal board to theungrounded terminal of the winding 42 of the motor SM. The plate andgrid circuits of the dual triodes 49 and 50 are interconnected toprovide a full wave rectifier, and a push-pull oscillator, of which thevariable inductance 53 comprises the tuning element. The filaments orheaters of the dual triodes are energized thrTough a separate secondary48 of the main transformer M The center tap of the secondary 8-1, 8-2,is connected by wire 46 to one terminal of the field winding 41 of themotor SM, the other terminal of which is grounded through to terminalboard TB-3. The network 47 comprises a by-pass circuit to ground for thealternating current components of the direct current output of therectifier, also provided by the dual triodes. The oscillator andrectifier circuits of the dual triode push-pull amplifiers andrectifiers are of themselves well known in the electronic arts.

This arrangement provides adequate power to operate the solenoid motorSM through the use of a push-pull control oscillator and rectifiercircuit. As is well known, in this arrangement the tubes operate on thepositive half cycle of their excitation and the current which flowsthrough them depends upon the grid bias which is a function of the radiofrequency voltage of the oscillating action.

The rectified component of each of the electron tubes is fed through thecoil 41 of the solenoid motor which is in the transformer center tabcircuit 46 to the cathode circuit of the amplifier. Movements of thebeam 13-14 of the magnetic balance tunes the high frequency oscillatorcoil 29 to control this current.

It will be noted that the winding 42, inductively related to the winding41, is connected to the balancing coil 84 of the galvanometer and,therefore, serves to measure the rate at which the magnetic field ischanging in the motor SM. The coil 84 applies a magnetic force to thegalvanometer beam which tends to oppose the change in movement thereofwhich the magnetic field of the input coil 12 is causing in response tothe input signal. This circuit is the stabilizing circuit for theinstrument and serves as the dampening means therefor. The rate ofchange at the output is measured and fed back inversely in a manner toreduce the speed at which the indicating pointer can move. Thus thetendency of the pointer to overshoot is minimized, and any tendency ofthe indicator pointer to oscillate is reduced.

By reason of the gearing up action of the Gold cord drive, very smallmovements of the armature 36 can be translated into ample movements ofthe pointer 23, thus providing for adequate scale indications with smallmovements of the armature of the solenoid motor SM.

As in the previous arrangement the spiral spring 20 serves to apply,through its connection to the pointer shaft 19, a calibrated mechanicalforce to the beam 13-14 to oppose its movements under the influence ofthe magnetic field of the input coil 12.

From this description and the embodiment of the invention hereindisclosed, it will be apparent that the objects of the invention as setout at the beginning of this specification are attained in a relativelysimple and practical manner. Those skilled in the art will appreciatethat changes in the details of construction and operation may be madewithout departing from the attainment of the objects of this invention.I do not, therefore, desire to be strictly limited to the specificembodiment of the invention herein disclosed.

What is claimed is:

1. In a system of the type described, the combination comprising meansproviding a fixed magnetic field, a pivotally mounted beam, an inputcoil in said magnetic field and connected to said beam, an oscillatorhaving a circuit the loading of which is varied by the actuation of saidbeam, a rotatably mounted shaft having a pointer, resilient means forinterconnecting said shaft with said beam, a motor energized by saidoscillator for rotating said shaft in one direction, and a springconnected to said shaft so as to be stressed, upon operation of saidshaft in upscale direction, to tend to operate the shaft in the oppositedirection, displacement of said pointer being proportional to the forceproduced by the application to said coil of the current to be measuredand as counterbalanced by the force produced by said resilient means.

2. In the combination of claim 1, said motor being a direct currentmotor, and means for rectifying the output of the oscillator to supplydirect current energization to said motor.

3. In the combination of claim 1, a second coil mounted on said beam,and means for supplying an induced current resulting from changes in thefield of said motor {30 said second coil to dampen the movements of saidearn.

4. In the combination of claim 1, means inductively associated with thefield of said motor for generating a current proportional to the rate atwhich the magnetic field of the motor is changing, and means mounted onsaid beam and connected to said last means to provide a magnetic forceopposing the movement of said beam by said input coil.

5. An indicating instrument comprising in combination a graduated scale,a pivotally supported pointer movable over said scale, a galvanometerhaving a resiliently supported beam, a magnetized field member and aninput coil attached to said beam and mounted in the magnetic field ofsaid member, a spring connecting said pointer to said beam, an electricmotor for driving said pointer upscale, a spring connected to saidpointer for driving it downscale, an electronic oscillator having atuning coil positioned adjacent said beam, means connected to said inputcoil for applying direct current signals to it, representing the valuesof a changing quantity to be measured, and circuit connections from theoutput of said oscillator to said electric motor for supplying anoperating current therefor.

6. In the combination of claim 5, means in said circuit connection forrectifying the output of said oscillator.

7. In the combination of claim 5, a second coil mounted on said beam andpositioned in the magnetic field of said member, and means connectedthereto and inductively associated with the field of said motor to applya counterbalancing force to said beam to stabilize its movements.

8. In the combination of claim 5, magnetic means mounted on said beamand energizing means therefor forming part of said motor for generatinga current varying in accordance with the rate at which the magneticfield of the motor is varying.

9. A measuring instrument combination comprising a pivoted pointer, anelectric motor for applying torque to said pointer to rotate it in onedirection, a spring acting to rotate said pointer in the oppositedirection, a force-balance galvanometer having a displaceable beam,magnetic means to be actuated by a direct current signal for applying adisplacing force to said beam, a calibrated spring connecting said beamand pointer, current generating means controlled by movement of saidbeam, and a circuit connecting said generating means to said motor.

10. In the combination of claim 9, said current generating meanscomprising an oscillator having a tuning element positioned adjacentsaid beam and controlled by its movements.

11. In the combination of claim 9, said current generating meanscomprising an oscillator having a tuning element positioned adjacentsaid beam and controlled by its movements, and a rectifier forrectifying the output of said oscillator.

- 7. 8 12. In the combination of clai$ 9, said current gen- ReferencesCited in the file of this patent crating means comprising an osc' atoraving a tuning element. positioned adjacent said beam and controlled 7UNITED STATES PATENTS by its movements, a rectifier for rectifying theoutput 2,005,884 Bemarde June 25, 1935 of said oscillator, a dampeningcoil connected to said 5 2,117,894 Lenehan May 17, 1938 beam, and meansforming part of said motor for sup- 2,154,260 Brandenburger Apr. 11,1939 plying energizing current to said coil proportional to 2,234,184MacLaren, Jr. Mar. 11, 1941 the rate of change of energization of saidmotor.

